1. Field of the Invention
The present invention relates to a method for producing carboxylic acid. More specifically, the present invention relates to a method for producing carboxylic acid that is useful as a polyester-based plasticizer or the like.
2. Background Art
Carboxylic acid is a useful substance that has been widely used as a starting material for polyester-based plasticizers, nylons, polyester materials, lubricating oil, and the like. There are a variety of known production methods thereof. In general, alcohol or aldehyde oxidation with the use of a metal compound such as potassium permanganate or potassium dichromate and oxidative cleavage of olefins with the use of an oxidant such as ozone have been conducted. However, since toxic substances such as metal compounds and ozone are handled when using such methods, there are still many problematic issues regarding industrial-scale production. In addition, in the case of a method using a metal compound, a large amount of waste containing heavy metals is generated due to poor selectivity, which is problematic. Further, in the case of a method using ozone, high electrical power is necessary for synthesizing a large amount of ozone. Therefore, the method is inappropriate for bioplastic material synthesis technology that contributes to the resolution of environmental problems.
Therefore, a recently known method for producing carboxylic acid is a method for producing carboxylic acid involving oxidative cleavage with the use of an oxidant such as hydrogen peroxide. For instance, JP Patent Publication (Kokai) No. 60-34929 A (1985) discloses a method for obtaining azelaic acid and pelargonic acid by allowing oleic acid to react with hydrogen peroxide with the use of a complex compound of phosphotungstic acid and quaternary amine as a catalyst. In addition, JP Patent Publication (Kokai) No. 63-93746 A (1988) discloses a method for producing azelaic acid and pelargonic acid from oleic acid as in the above case with the use of heteropoly acid as a catalyst. However, in terms of industrial practice, these methods are disadvantageous, for example, in that they require complicated operations, and in that the production cost is high.
Further, JP Patent Publication (Kokai) No. 5-4938 A (1993) discloses that saturated carboxylic acid can be obtained at a good yield through simple production steps even with the use of low-concentration hydrogen peroxide by carrying out an oxidative cleavage reaction for oxidation of unsaturated carboxylic acid with hydrogen peroxide, provided that tungstic acid, phosphotungstic acid, or the like and a quaternary amine salt are separately added to the reaction system.
The above conventional techniques are insufficient for practical use due to, for example, the following reasons: dicarboxylic acid cannot be synthesized directly from a starting material which is a plant seed oil such as triolein or plant oil such as canola oil or carrot oil; and tricarboxylic acid has not been successfully synthesized. Tricarboxylic acid is a trifunctional monomer and is useful as a crosslinking agent for bioplastics. However, it has been difficult to produce tricarboxylic acid by conventional synthesis methods involving the use of petroleum as a starting material.